This invention relates to an improved motion sensor for sensing motion and thus providing positional information for moving components positioned in high pressure fluid in a fluid delivery device, such as a high pressure fuel pump or injector.
As a result of stringent government fuel consumption and emissions regulations, fuel injection pressure, timing and quantity control has become even more important to optimize combustion and meet the regulatory requirements. Also, precise diagnostic information relating to fuel system operation provides valuable data for monitoring and controlling fuel system and engine operation. The measurement of fuel delivery plunger and control valve element motion and/or position provides valuable information for diagnostic evaluation and feedback control to assist in optimizing engine operation. In most high pressure fuel systems applicable to internal combustion engines, high pressure fuel delivery devices, such as fuel injectors and fuel pumps, incorporate various reciprocating members used to pressurize fuel and/or control fuel delivery. For example, a reciprocating high pressure plunger may be used to increase the pressure of supply fuel to a high pressure level for injection. Also, control valve elements, such as a needle valve element in a closed nozzle injector or an injection control valve element of an electronically controlled injection valve, are used to control the flow of fuel for injection or for injection timing/quantity control purposes.
Both plungers and control valve elements reciprocate at very high frequencies during operations. For example, a needle valve for a closed nozzle injector is opened and closed at appropriately timed intervals to inject desired amounts of fuel into a cylinder of an internal combustion engine, such as a diesel engine. It is important to know when the needle valve opens in relation to the engine crank shaft position to ensure the appropriate injection timing. When the needle valve is lifted off the needle seat, the valve opens and fuel is metered through spray orifices into the interior of the engine cylinder. The initial relative axial displacement between the needle and the needle seat determines the beginning of injection as well as the engine ignition timing.
U.S. Pat. No. 4,359,895 to Wolff et al. discloses a needle position indicator for a fuel injector including a Hall effect sensor positioned within a spring cavity containing a spring for biasing the needle valve into a closed position. The Hall effect sensor is mounted on a cylindrical bracket a spaced distance from an outer end of the needle valve element. The Hall effect sensor is positioned between a three lead header and a layer of epoxy encapsulation. A magnet is mounted on the outer end of the needle valve element to generate a magnetic field. The sensor detects changes in the strength of the magnetic field within the cavity caused by relative displacements of the upper portion of the needle. However, the spring cavity is continuously connected to drain and therefore maintained at a low fuel pressure. Consequently, the sensor assembly is not specifically designed to withstand high pressure forces nor to prevent fuel leakage around the sensor assembly. In addition, the sensor requires a magnet attached to the needle valve element thereby undesirably requiring additional components, manufacturing/assembly costs and potential malfunction or damage due to dislodging of the magnet.
Consequently, there is a need for a sensor and a fuel injector incorporating the sensor that effectively and reliably senses plunger/valve element motion while withstanding high fuel pressure forces and tending to prevent fuel leakage around the sensor.
It is an object of the present invention, therefore, to overcome the disadvantages of the prior art and to provide a sensor for a high pressure fluid delivery device capable of effectively sensing plunger or valve element movement.
It is another object of the present invention to provide a sensor designed with a shape that complements the receiving cavity in a high pressure cavity wall so as to minimize the likelihood of fuel leakage through the cavity.
Another object of the present invention to provide a high pressure fuel delivery device and a displacement sensor positioned in the device such that the fuel pressure forces applied to the sensor push the sensor into sealing contact with the device.
It is yet another object of the present invention to provide a simple and inexpensive sensor capable of maintaining structural stability when subject to very high pressure fuel forces.
It is still another object of the present invention to provide a displacement sensor for high pressure delivery devices that solves the problem of sensor sealing at high pressure.
It is a further object of the present invention to provide a sensor that can be easily and precisely installed and is capable of withstanding high pressure, rapidly changing temperatures and a high vibration environment.
Still another object of the present invention is to provide a sensor for an injector which minimizes design changes to existing injector designs to achieve effective integration of the sensor.
Yet another object of the present invention is to provide a method of forming and installing a displacement sensor for determining the motion of a plunger/needle in a high pressure assembly including the steps of forming a specially shaped sensor receiving cavity opening into a high pressure cavity in which the plunger is mounted and forming the sensor to withstand the high pressure with a shape that complements the receiving cavity whereby the force applied to the sensor by the high fluid pressure pushes the sensor into sealing contact with the sensor receiving cavity.
These and other objects of the present invention are achieved by providing a motion sensor at least partially positionable in a sensor receiving cavity, formed in a high pressure fluid delivery device and defined by an annular cavity surface, for sensing motion of a movable component in the fluid delivery device while being exposed to high fluid pressure forces, wherein the fluid delivery device includes a force resisting surface formed in the sensor receiving cavity. The motion sensor comprises a sensor body shaped for positioning in the sensor receiving cavity in contact with the annular cavity surface, wherein the sensor body includes a sealing surface shaped and positionable to apply a fluid pressure induced sealing force to the force resisting surface due to the high fluid pressure forces acting on the sensor body to prevent high pressure fluid leakage through the sensor receiving cavity. Some portion of the motion sensor, e.g. the sensor element and/or sensor leads/conductors, is securely mounted in the sensor body and positioned in the sensor receiving cavity. The sealing surface may be conically shaped and extend along substantially an entire length of the sensor body. Alternatively, the sealing surface may include a conically shaped portion and a nonconically shaped portion. The sensor body may include a core portion containing the sensor element and an extension portion extending from the core portion wherein the sealing surface is formed on one end of the core portion and extends annularly around the sensor body. In this case, the core portion may be formed of ceramic material and the extension portion formed of an epoxy material. The core portion may be cylindrically shaped and the extension portion conically shaped, wherein the sealing surface is formed on the conically shaped extension portion. Also, the extension portion may have a smaller radial extent than the core portion. The core portion may also include a sensor element cavity containing the sensor element and having an axial extent greater than the sensor element. The sealing surface may be positioned axially along the sensor body a spaced distance from the sensor element. The motion sensor may further include surface variations formed on an outer surface of the sensor body for engaging complementary variations on the annular cavity surface to enhance secure mounting of the sensor body in the receiving cavity. The surface variations may be annular threads. The sealing surface may extend radially and annularly along a plane perpendicular to a longitudinal axis of the sensor body.
The present invention is also directed to a high pressure fuel delivery device comprising a fuel delivery device body including a high pressure chamber containing high pressure fuel, a sensor receiving cavity opening into the high pressure chamber and a force resisting surface positioned in the sensor receiving cavity. The high pressure fuel delivery device further includes a movable component mounted for reciprocal movement in the high pressure chamber and a motion sensor at least partially positioned in the sensor receiving cavity while being exposed to high pressure fuel forces due to the high pressure fuel in the high pressure chamber. The motion sensor includes a sensor body shaped for positioning in the sensor receiving cavity and a sensor element securely mounted in the sensor body. The sensor body includes a sealing surface shaped and positioned to apply a fuel pressure induced sealing force to the force resisting surface during operation of the high pressure fuel delivery device due to the high fuel pressure forces acting on the sensor body to prevent high pressure fuel leakage through the sensor receiving cavity. The sensor receiving cavity may extend through at least a portion of the fuel delivery device in a direction transverse to a longitudinal movement axis of the movable component. The sensor receiving cavity may be defined by an annular cavity surface wherein an outer surface of the sensor body is sized and positioned in annular contact with the annular cavity surface and the force resisting surface is formed on the annular cavity surface. The force resisting surface may be at least partially conically shaped so that an entire length of the force resisting surface may be conically shaped. The force resisting surface may be formed on an annular land extending in a plane transverse to a longitudinal axis of the sensor receiving cavity. The sensor body may include a core portion containing said sensor element in an extension portion extending from the core portion wherein the sealing surface is formed on one end of the core portion and extends annularly around the sensor body. Surface variations may be provided in the annular cavity surface for engaging complementary variations on the outer surface of the sensor body to enhance secure mounting of the sensor body in the receiving cavity.
The present invention is also directed to a method of installing a motion sensor in a high pressure fuel delivery device for sensing the motion of a movable component positioned in the delivery device, comprising the steps of providing a fuel delivery device body including a high pressure fuel chamber for receiving the movable component, a sensor receiving cavity opening into the high pressure fuel chamber and a force resisting surface positioned in the sensor receiving cavity, and providing a motion sensor for sensing motion of the movable component wherein the motion sensor includes a sensor body including a sealing surface shaped to annularly abut the force resisting surface. The method further includes the step of positioning the motion sensor in the sensor receiving cavity with the sealing surface in abutment against the force resisting surface wherein the sealing surface and the force resisting surface are shaped and positioned to cause the sealing surface to apply a fuel pressure induced sealing force to the force resisting surface due to high pressure forces acting on the sensor body during operation of the high pressure fuel delivery device to prevent high pressure fuel leakage through the sensor receiving cavity.